Solid-phase microextraction (or “SPME”) is an analytical technique that uses a fluid polymer phase, a solid adsorbent, or a combination of the two, immobilized or coated on a fused silicon fiber. The coated fiber (hereinafter referred to as an “SPME fiber”) is immersed in a liquid sample, or in the headspace above the sample, to absorb the analytes of interest, which are subsequently desorbed with the aid of heat in a gas chromatograph injector and thus transferred to a capillary column. The selectivity of this technique may be varied by changing the type or thickness of the phase coating on the fiber. This analytical method has found widespread use in various fields, being used for biological and environmental analyses, toxicology and in the agro-food sector.
An SPME unit essentially has two parts: (1) a probe comprising coated fused silicon fiber attached at one end to a plastic connector and housed slidingly in a needle such that the opposite end of the fiber may be exposed, and (2) a tubular, syringe-like container having a plunger threadably engaged with the connector. Sliding action of the plunger causes a larger or smaller portion of the fiber to extend from, or withdraw into, the needle. The analyte may be extracted either by exposing the coated portion of the fiber to the headspace of a test tube, immersing it in a fluid (e.g. water, milk, fruit juices, wines, etc.), or by exposing the fiber to air (for instance, in a working environment where the concentration of airborne pollutants is to be measured).
Generally speaking, there are three types of probe containers (hereinafter referred to as “holders”) namely, holders for (i) manual analyses, (ii) field tests, and those for (iii) automatic samplers (or “autosamplers”). An autosampler is a well-known apparatus having a robotic arm that allows the user to automatically extract the analyte (i.e., conduct sampling) and inject it into the gas chromatograph. While conventional autosampplers have been found useful, the user must intervene each time a coated fiber must be replaced which, depending on the class of compounds being assayed, may require that fibers of different phases be immobilized. In such cases, the samples to be analyzed may be housed in test tubes inserted in suitable support plates that are accessible to the sampling head of the robotic arm.
Although SPME has been found beneficial, automation of the extraction/injection process is often limited because of the necessity that the user intervene each time the probe, installed on the autosampler arm, must be changed. There are, indeed, situations, when the probe has to be replaced after each injection in the gas chromatograph, making automated analysis unfeasible. Such is the case, for example, in determining levels of airborne pollutants as,  during a given sampling campaign, technician collecting samples is likely to return to the laboratory with a large number of probes whose fibers have been exposed to the environment or are being monitored. In this type of analysis, the number of fibers depends on the number of sampling points chosen, and on the number of individuals working, in the area being monitored. Specifically, one or more probes may be attached to the workers' clothing to assess their exposure to airborne pollutants.
In environmental analyses, each SPME probe is effectively equivalent to a testtube that users of conventional arrangements must always change inside the holder before they can inject the sample into the gas chromatograph. Using When using holders currently available on the market, while SPME fibers can be used on some autosamplers, multiple fibers cannot be used simultaneously in a single working session unless the autosampler is stopped and an operator is on hand to change the probe. Moreover, where each fiber represents a selected sampling point, there is generally no difference—in terms of timesaving—between injecting the analyte through the port by hand or installing the fiber of the holder in the autosampler. Unfortuneately, if, for instance, there are two sets of samples on which two substances must be assayed, that require two different SPME fibers, then the first set of samples must be analyzed first, and, subsequently, the fiber changed before the second set of samples can be analyzed. Although this issue is already problematic with assays on liquid or biological samples, it becomes magnified during environmental sampling, when the absence of a fully automated procedure increases considerably the time necessary to perform the analyses.